Fix BiDi directionality for surrogate pair characters

third_party/WebKit/Source/core/layout/LayoutText.h

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004-2009, 2013 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 307 matching lines @@
 }
 
 inline UChar LayoutText::characterAt(unsigned i) const {
   if (i >= textLength())
     return 0;
 
   return uncheckedCharacterAt(i);
 }
 
 inline UChar32 LayoutText::codepointAt(unsigned i) const {
-  UChar32 character = characterAt(i);
-  if (!U16_IS_LEAD(character))
-    return character;
-  UChar trail = characterAt(i + 1);
-  return U16_IS_TRAIL(trail) ? U16_GET_SUPPLEMENTARY(character, trail)
-                             : character;
+  if (i >= textLength())
+    return 0;
+  if (is8Bit())
+    return characters8()[i];
+  UChar32 c;
+  U16_GET(characters16(), 0, i, textLength(), c);
+  return c;
 }
 
 inline float LayoutText::hyphenWidth(const Font& font,
                                      TextDirection direction) {
   const ComputedStyle& style = styleRef();
   return font.width(constructTextRun(font, style.hyphenString().getString(),
                                      style, direction));
 }
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutText, isText());
 
 #if !ENABLE(ASSERT)
 inline void LayoutText::checkConsistency() const {}
 #endif
 
 inline LayoutText* Text::layoutObject() const {
   return toLayoutText(CharacterData::layoutObject());
 }
 
 void applyTextTransform(const ComputedStyle*, String&, UChar);
 
 }  // namespace blink
 
 #endif  // LayoutText_h